A postprocess volume broke the technique I was using before to set depth-of-field postprocess settings. So this is what I do now:
function UpdateDOF()
{
local PostProcessSettings OverrideSettings;
local PlayerController PC;
PC = GetALocalPlayerController();
// Calculate DOF settings...
OverrideSettings.bEnableDOF = true;
OverrideSettings.bOverride_DOF_FocusDistance = true;
OverrideSettings.DOF_FocusDistance = // ****** calculate DOF_FocusDistance ******
OverrideSettings.bOverride_DOF_FocusInnerRadius = true;
OverrideSettings.DOF_FocusInnerRadius = // ****** calculate DOF_FocusInnerRadius ******
OverrideSettings.bOverride_DOF_FalloffExponent = true;
OverrideSettings.DOF_FalloffExponent = // ****** whatever you want the FalloffExponent to be ******
OverrideSettings.DOF_InterpolationDuration = 0.0;
LocalPlayer(PC.Player).OverridePostProcessSettings(OverrideSettings);
}